1. Field of the Invention
The present invention relates to a fuel cell vehicle system.
2. Description of the Related Art
A solid polymer membrane fuel cell conventionally includes, for example, cells formed by sandwiching a solid polymer electrolyte membrane between a fuel electrode (anode) and an oxygen electrode (cathode), with a plurality of such cells arranged in a stack. Hydrogen is supplied to the fuel electrode as fuel, and air is supplied to the oxygen electrode as oxidant, and hydrogen ions generated by a catalytic reaction at the fuel electrode pass through the solid polymer electrolyte membrane and migrate to the oxygen electrode, causing an electrochemical reaction with the oxygen at the oxygen electrode, and generating electricity.
As a fuel cell vehicle provided with such a fuel cell as a source of motive power, heretofore there is known a fuel cell vehicle, fitted with a capacitor including for example an electric double layer capacitor or an electrolytic capacitor or the like, and constructed so as to store the electrical energy generated by the fuel cell, and transfer electrical energy to the propulsion motor (see for example, Patent document 1).
In such a fuel cell vehicle, the capacitor is connected in parallel to the fuel cell via an output controller which controls the output current and output voltage of the fuel cell, and output control action such as chopping action or the like of the output controller which includes, for example, a chopper type power conversion circuit, is controlled corresponding to the state of, for example, the fuel cell vehicle, the fuel cell, or the capacitor.
[Patent document 1] Japanese Unexamined Patent Application, First Publication No. 2001-357865.
In practice, at the time of travelling and the like of the fuel cell vehicle according to the example of the aforementioned technology, in the case of a condition where the output current extracted from the fuel cell is not restricted by the output controller, that is the fuel cell and an energy storage device (e.g., a capacitor, battery, etc.) are in a directly connected condition, the terminal voltage of the energy storage device and the output voltage of the fuel cell become the same value.
Therefore, if for example the energy storage device is charged by the regeneration of the propulsion motor, then both the terminal voltage of the energy storage device and the output voltage of the fuel cell increase. At this time the setting is such that a command value for the output current corresponding to the increased output voltage based on predetermined power generation characteristics for the output current and output voltage, is input to the fuel cell, so that the relative relationship for the output current and the output voltage does not deviate from a predetermined power generation characteristic.
However, in the case where during regeneration of the propulsion motor, the power generation of the fuel cell continues, and for example the regenerative electric power of the propulsion motor is greater than the chargeable power which can be charged to the energy storage device, there is the possibility that unnecessary power generation continues, so that the energy efficiency of the fuel cell vehicle drops.